The invention relates to an indicator device and method for determining whether a soil is hydric.
Natural wetlands collect and purify surface water before it reaches the streams and aquifers that provide our drinking water. They also serve as habitats for many birds and animals, and they provide areas for recreation. We have drained or developed most of the wetlands in the U.S. In recent years, however, Americans decided, through congressional action, to preserve our remaining wetlands. Because wetland cannot be drained or developed, there is much interest in whether or not a specific tract of land qualifies as a wetland. This device will help wetland delineators make that decision.
In 1987 the Army Corps. Of Engineers published the Wetland Delineation Manual in response to federal legislation mandating the protection of wetlands. Additional federal publications for identifying and delineating wetlands 59 FR 35680, Jul. 13, 1994, and 60 Fr 10349, Feb. 24, 1995 were published. According to the documents, wetlands cannot be drained or destroyed by development under penalty and or special mitigation requirements. Jurisdictional wetlands have three essential requirements: hydric soils, hydrophytic vegetation, and wetland hydrology. By definition, hydric soils are those that are saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions in the upper part. That is, hydric soils have a water table at or near surface for a time long enough during the growing season to become anaerobic. In saturated soils anaerobic microorganisms use compounds such as nitrate, manganese oxides and/or iron oxides as an electron acceptor instead of oxygen in respiration processes. A byproduct of this microbial activity is the increased mobility of Mn and Fe in the soil solution. The saturated conditions of the hydrology factor, the soil oxygen deficiency of the vegetation factor, and the anaerobic conditions of the soil factor are all related (Franzmeier, D. P., E. J. Kladivko, and B J Jenkinson. 2001. Drainage and Wet Soil Management. Purdue University Cooperative Extension Service).
An object of the invention is to provide an indicator device and method for determining whether a soil is hydric.
The present invention provides an indicator device that is adapted to be disposed in the soil and that exhibits a change in color when exposed to anaerobic conditions over time. In an illustrative embodiment of the invention, the indicator device comprises a substrate having an indicator coating thereon that is at least partially removable from the substrate at one or more regions of the coating when the indicator device is exposed in the soil to anaerobic conditions over time so that indicator device changes color at the one or more regions. The indicator coating is not removed when the device is exposed to aerobic soil conditions. The indicator device is removed from the soil for visual inspection to determine its color change.
In an illustrative embodiment of the invention, the substrate comprises a PVC (polyvinyl chloride) tube or sheet coated with a coating of iron or other metal oxide, such as for example, ferrihydrite, such that, when the indicator device is installed in a soil and exposed to sustained anaerobic conditions, the oxide coating will be removed at least partially through its thickness at one or more regions and ultimately may expose the underlying white PVC substrate, thereby providing a visual indicator in the field that reducing soil conditions were present.